Touch sensor devices (also commonly called touch pads or touch screens) are widely used in a variety of electronic systems. A touch sensor device is typically a sensitive surface that uses capacitive, resistive, inductive, optical, acoustic or other technology to determine the presence, location and or motion of one or more fingers, styli, and/or other objects. The touch sensor device, together with a finger or other object provides an input to the electronic system. For example, touch sensor devices are used as input devices for computers, such as notebook computers.
Touch sensor devices are also used in smaller devices, such as personal digital assistants (PDAs) and communication devices such as wireless telephones and text messaging devices. Increasingly, touch sensor devices are used in multimedia devices, such as CD, DVD, MP3, video or other media players. Many electronic devices include a user interface (UI) and an input device for interacting with the UI. A typical UI includes a screen for displaying graphical and/or textual elements. The increasing use of this type of UI has led to a rising demand for touch sensor devices as pointing devices. In these applications the touch sensor device can function as a cursor control device, selection device, scrolling device, character/handwriting input device, menu navigation device, gaming input device, button input device, keyboard and/or other input device.
One challenge in touch sensor device design is differentiating between deliberate input and incidental contact to the touch sensor device. This is particularly true for wireless communication devices, such as mobile phones. For example, when a user holds a mobile phone near their face to conduct a phone call, the touch sensor device might register input to the mobile phone if the user's face (e.g., cheek) contacts the touch sensor device. As such, when a user holds a mobile phone near their face to conduct a phone call, it may be desirable to deactivate the touch input support while the user is making a call.
Typically, an independent sensor (e.g. infrared sensor) is used for the purpose of detecting the proximity of the user to the sensing region and disabling or otherwise suppressing input in the sensing region of the input device. However, infrared sensors and their supporting circuitry increase the manufacturing costs and are limited to detecting objects in a pre-defined position relative to the infrared sensor. Further, a separate subsystem for the infrared sensor may take up additional space within the electronic system which already faces substantial space and size constraints.
Therefore, there is a need for an improved input device, processing system, and method for sensing an input object relative to a sensing region of a touch sensor device.